Stiles would be canonically bi and we'd see him with a guy (doesn't have to be Derek because that would be horribly OOC at this point)
More canonically gay/bi characters in general.
Veronica wouldn't have gotten back together with Duncan and never would have dated Piz. She and Logan would both do some growing up before trying again.
If we're counting other media too, there are so many things I'd change about the Anita Blake series by Laurell K Hamilton.
The third and fourth movies in the Alien series wouldn't suck and would live up to the first two.
Re: Things you'd change in canon
Stiles would be canonically bi and we'd see him with a guy (doesn't have to be Derek because that would be horribly OOC at this point)
More canonically gay/bi characters in general.
Veronica wouldn't have gotten back together with Duncan and never would have dated Piz. She and Logan would both do some growing up before trying again.
If we're counting other media too, there are so many things I'd change about the Anita Blake series by Laurell K Hamilton.
The third and fourth movies in the Alien series wouldn't suck and would live up to the first two.